


The Flooded Caverns

by Daemont



Category: Undertale (Video Game)
Genre: Anthropomorphic, Breasts, Child Frisk (Undertale), Drowning, F/M, MILFs, Male Frisk (Undertale), Nudity, Peril, Shotacon, Skinny Dipping, Underwater
Language: English
Status: In-Progress
Published: 2020-09-30
Updated: 2020-10-11
Packaged: 2021-03-07 16:02:14
Rating: Explicit
Warnings: Underage
Chapters: 2
Words: 3,300
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/26730334
Author URL: https://archiveofourown.org/users/Daemont/pseuds/Daemont
Summary: Toriel and Frisk find themselves transported to a system of caves, and are lost, naked and alone in a cave where the only means of escape is a network of flooded tunnels. Will they find a way out to freedom, or succumb to the depths?
Relationships: Frisk & Toriel (Undertale)
Kudos: 17





	1. Waking Up

There was a cold chill running through the deep, dark caves, as if something was disturbed in its untouched habitat. The gentle dropping of water onto the wet, rocky ground echoed through the walls of the cave, as sunlight bled through the large hole in the ceiling high above, an almost inverted funnel shape making escape near impossible if one were to climb the rocky walls. 

However, in this near tranquil cave, lay the naked, unconscious figures of a female boss monster, and a young, human child. Blinking wearily, Toriel awoke with a bleary yawn, her vision clearing as she noticed her unusual surroundings. Last thing she remembered, she was sleeping calmly with Frisk in a hotel room, the two having taken a short vacation together in the tropics. But, there was a blast of magic as the door to their room burst open and then… nothing.

Toriel sat up, looking around at the cave interior as the sun beamed down on them from the hole. She looked down to see herself naked, which made her naturally cover her modesty, her chubby figure on display, fur nearly glistening in the sun. But once she realised she was alone, she dropped her cover, her breasts giving a little jiggle, pink nipples erect from the chill. Then, she noticed a heavy sensation on her leg and looked down to see Frisk lying on it, just as naked as she was! 

She grabbed the child's shoulder and began shaking him, her voice filled with mild worry, "Frisk, wake up! Please, my child, wake up!" 

With a mild groan, Frisk leaned up, putting his hand on her plush thigh as he rubbed his eyes with the other. He spoke out in annoyance, unaware of his current situation, "I'm up, I'm up… Geez, what's the yelling for, mom?" 

Giving a sigh of relief, her hand remained on his shoulder, "Thank goodness you are okay, Frisk. I was worried you were hurt!" 

Confused, Frisk tilted his head, "What are you talking about? What's… wrong?..." His voice trailed when he happened to notice that the warm, coziness of their hotel room was instead replaced with a cold, almost alien cave. "What's going on? Where are we?!" He sprang to his feet, looking around as a rush of adrenaline shot through him. 

Toriel also stood to her feet, walking to the child, "Frisk, remain calm!" She looked very concerned, but didn't want to worry Frisk by worrying herself. She looked up to the hole and let out a yell, "Hello?! Is there anyone up there?!" A cold silence greeted them, the dripping of the stalactites being their only reply. She tried again, "HELLO?! IS THERE ANYONE WHO CAN HELP?!" 

The echoing bellows of her call made Frisk cover his ears. "Geez, I'm right here, mom!" He said to her, making the goat cover her mouth in mild embarrassment. He looked up and said, "Do you think you could try some magic, mom? Maybe teleport or levitate us out?" 

She shook her head, "I am sorry, my child, but I do not possess that kind of power. I know Sans has such a power, but how he does that is such a mystery…"

Frisk let out a frustrated moan, "So we're stuck down here, is that it?" He walked towards Toriel, his bare feet splashing against the small puddles on the rocky floor. 

"Frisk, calm yourself! This is not the time to give up." She said sternly, making the child pipe down for a moment. "Let us look around and find a means of escape." She looked around and saw a hole in the wall, "Look, over there."

Walking towards it, Frisk followed as the boss monster inspected the hole, light from above illuminating the other side, but what was inside she couldn't make out, "Hmm, looks like it will fit me…" She stood aside, "You go first, my child. Tell me what you see." 

Frisk nodded and climbed up to the hole, Toriel lifting his foot up to give him a boost, giving his nude butt a little push to help him through. He clambered easily through the hole and dropped out to the other side. "What do you see in there, Frisk?" She called through the hole. 

He looked back through the hole, calling to his mom, "There's a pool of water here! Not much else, though."

Toriel then cambered through the hole herself, her plump figure definitely giving her a slight reminder to cut out the pie-making every once in a while. Her body and curves nipped and pinched on the rocky surroundings, but the goat managed to squeeze through as she dropped to the floor, Frisk giving her a hand up, "Thank you, sweetheart." 

In this other room, there was a large body of water on the other side, and a large shore leading into it. Thanks to her being much taller than Frisk, she could see something that the child couldn't. There seemed to be a tunnel located in the lake, submerged a little under the surface. She put a hand to the child's head and walked towards the water, "Wait here, my child." 

Feeling the water lap against her feet, the goat walked in slowly and steadily, making sure to keep an eye on what she could be stepping on. Frisk called out, "Is it okay, mom?" 

She looked behind her to reply, "The water's kind of warm! I wonder how deep it goes…" Toriel then walked further, the water climbing up her thighs, to her hips and eventually her upper body. Frisk watched with bated breath as his mom walked calmly into the water, her nude figure on display for the child. 

Suddenly, Toriel dropped and landed in the water with a mild yelp, submerging under the surface. "Mom!" Frisk yelled out, running to the water as he walked out until it reached to his knees, "Mom, are you okay?! Mom!" There was no reply, Frisk started to get more worried, "Mom, answer me!" 

Then, Toriel surfaced with a gasp, shaking the water from her fur as her ears flopped side to side. She turned to the child, "I'm okay, Frisk! The shore suddenly dropped into the depths there." She let out a mild giggle at her misfortune, Frisk letting out a sigh of relief. 

"Don't scare me like that, mom." He replied, noticing the tunnel under the surface and pointed to it. "Is that a tunnel there?" 

Looking, the boss monster gave a mild murmur of thought. She then began to swim out, "Wait there, Frisk!" She took a deep breath and submerged under the surface. Pumping her arms, she swam towards the tunnel and put a hand to the rim, looking inside. The tunnel was mildly bright, and the water was surprisingly clear, the goat able to see quite far in before things got blurry. The goat even noticed a slight change in temperature as she peered into the cave, indicating a possible exit. She gave a confirming nod and pushed off the rock with her feet, a few air bubbles leaking from her pursed lips. 

Breaching the surface with a gasp, she swam up to Frisk, "Well, the tunnel does lead somewhere. But it will be quite a dive before we find a way out." 

Frisk then paused for a moment and replied, "So, we'll have to swim through it." Toriel nodded and looked quite despondent. She didn't want anything to happen to Frisk, let alone possibly drown in the depths of this tunnel, not even thinking about herself and how she would even cope. Frisk too worried about drowning in this tunnel, but if it meant that the only way out was to swim, he wasn't going to sit here and mope about it. "I'll do it." 

Toriel noticed and looked to him, "My child?" She was surprised that Frisk seemed so suddenly brave to take this potentially lethal dive with her, but given that if it weren't for him, the monsters wouldn't even be on the surface, it shouldn't have been too surprising. "My child, will you be alright? I am alright to go by myself and get help, you do not need to put yourself in danger." 

He shook his head, "I don't want anything to happen to you, mom. I'm only a kid, but I've been through worse. Plus, I've also been swimming with Undyne back home. I'll be okay mom, I promise." He gave a trusting smile, a smile Toriel could not simply ignore. 

She gave a sigh and smiled at the young child, the brave little man who would accompany her on this perilous dive, "Okay, come with me, Frisk." She held out a hand as Frisk walked forward, swimming as the water climbed up and took her paw, now face to face with her adopted son, only eight years of age but what felt like a brave warrior to her eyes. 

She held onto his hand as she looked to him, speaking seriously, "Now my child, this will potentially be a very long dive, and I cannot guarantee that we will find any means of air. I want you to take the biggest, deepest breath you can, and I don't want you to let go of it until I tell you to. Remember, if you feel that your lungs are hurting, simply let go of some air and hold onto the rest. I will help you however I can. Will you be a big boy for me, Frisk?"

Frisk gave a confident nod," Sure I will, mom!" His smile was infectious as she gave a small giggle herself, feeling more confident about their upcoming trial. 

Toriel hugged the child close, kissing his forehead, "Mommy loves you, Frisk…"

"Love you too, Momma…" He returned the gesture, kissing her cheek. 

Soon, the two were taking deep breaths, breathing in and breathing out. Toriel made sure Frisk got his breaths in, "Breathe in… and out. There we go." Once she was ready, Toriel swam towards the tunnel and began counting, "Ready, my child? One… Two…" 

"Three!" They called out, sucked in a deep breath and dove together under the surface. Toriel put a hand to his back to help Frisk swim underwater, to make sure his buoyancy didn't hinder him. She felt the cool waters brush against her fur, the goat blinking to clear her vision. Her nipples stood further on end, the child feeling his erection start to grow thanks to the chill of the waters. 

But, none of this really hindered their swim, the two making a steady swim through the tunnel as they swam into its depths. The goat and her child were ready to tackle whatever lay ahead of them. But, it wouldn't be too long before they were put to the test, to push them to their limits… 

To see if they would drown within the depths…


	2. The First Stretch

**Summary for the Chapter:**

> Now that Frisk and Toriel are within the depths of the caves, they both explore their new surroundings, with young Frisk discovering what his limits are.

With a breath, Toriel and Frisk both submerged and began swimming into the tunnel, their naked bodies cutting through the cool, clear water with relative ease. They were both determined to make their way out of the caves they were dumped in after a strange, magical attack knocked them unconscious and were both dumped in a hole. They didn't know or even care who tried to get rid of them like this, but the two only wanted to escape with their lives. 

Looking to her side, Toriel had her hand planted on Frisk's back, to make sure that his buoyancy didn't start lifting him up to the ceiling. However, he seemed pretty controlled underwater, thinking that Undyne must've taught him a few swimming tricks and techniques. She gave a smile and lifted her hand, Frisk looking to her with a smile past his pursed lips, a few bubbles leaking from his nose. 

She returned the smile and looked on ahead, swimming by the child's side as her arms and legs pumped through the water, much like how a frog would swim. However, this caused her to start swimming ahead of the child, making Frisk swim harder to catch up. She did look to see he had fallen behind and slowed so he could catch up. Fortunately, the tunnel gave the two ample room to move around in, at least for the moment, so they could reorient and adjust without issue. 

Toriel kicked her legs slowly, pumping her arms as Frisk copied her motions, and the two were able to swim together at a more comfortable speed. The child felt her large, furry hand brush against his smooth, tan skinned body, not much to get in the way, but enough for him to notice and feel somewhat safe in Toriel's company. However, his lungs gave him a brief reminder that he needed to breathe.

Putting a hand to his mouth, Frisk exhaled a bit of air from his lips just as his mother instructed, which was enough to relieve the pain for a little while. Toriel could quite comfortably hold her breath for a while, she hadn't really timed herself to see how long she'd last, but she knew that Frisk would have difficulty staying under this long. 

As the tunnel curved to the right, the child's motions became a bit more unfocused, his arms starting to flail like he was doing a doggy paddle. His lungs were starting to hurt, even with the air he let go to try and relieve the pressure, but it just kept hurting. He put a hand to cover his mouth as a plume of air bubbles escaped his mouth in an o-shape. Toriel immediately took notice and took his hand, swimming faster as she looked around desperately for any kind of air or place to breathe. 

Swimming deeper, the goat wouldn't have to wait much longer, as a small pocket of air glistened just up ahead. She pointed it out to her son and helped him up to it. Frisk was already starting to convulse from the lack of air, pinching his nose and puffing his cheeks. Toriel came to the pocket, a small crack just big enough to put your mouth into, and least for Frisk definitely. 

Frisk felt her hand cup the back of his head as he was pushed onto his back, and helped to the pocket. He felt his nose and mouth breach the surface as he gasped desperately for air, "PAAAAH!" He coughed up some water and took the air in, putting his hands against the rock to steady himself, "I c-- I can't hold on for too long mgh- Momma! But… I'll keep trying!" He said, trying not to get water into his mouth as his breathing soon calmed.

He took a deep breath and submerged again, looking much more comfortable than he did just before. Toriel smiled and felt a burst of air rip through her nose, and gave a bashful smile before putting her mouth to the hole and taking in the air. "You are doing ever so well, Frisk! Mommy is so proud of you! We must keep going, hold those breaths, my child!" 

She knew that they couldn't stay as the CO2 buildup would become too much before long in an enclosed pocket like this, so took a deep breath and submerged again. She swam with Frisk by her side, the child grabbing her shoulder to help propel himself before swimming independently again.

Watching her adopted son swim with such ease despite his young age gave the goat some form of relief, not having to worry too much about having to help, but as he didn't have as strong a breath holding capacity as she did, he would obviously need some extra support. 

Frisk looked at Toriel, seeing that her eyes were upon him, made her blush a little before focusing on the path ahead. They soon came to a large chamber, with what seemed to be a hole in the ceiling providing mild sunlight, the ceiling sloping up to it. The goat swam over and inspected it, hoping it would be a possible means of escape. 

She turned her body to get a closer look, showing her bare front to Frisk, large breasts accompanying a plump, yet voluptuous figure. Her legs spread as she kicked to reveal her folds, making the child deeply blush as he tried to look away. Despite being his adoptive mother, he had seen her naked a few times before, namely while swimming in the lake back home or sleeping on those warm, summer nights, and each time he was filled with a sense of warmth and maybe even a little love… 

Frisk shook his head, surely he couldn't love his adoptive mother like that? He looked to Toriel again, trying to avert his eyes from her brazen nudity, but was distracted when she pushed herself back down and shook her head. The hole was too small for either of them to escape through. Frisk looked around and saw the passage stretching on ahead and nodded to Toriel before swimming again, bubbles leaving his nose in small bursts. 

But, as they swam, Frisk started to slow down a little, and tried to push himself forward but his body was slowing, like he was trying to swim in syrup. While he could quite comfortably swim underwater, he didn't exactly have the strength to keep swimming long distances underwater, especially with no visible end in sight. He paddled to try and keep up, but it was obvious that he was slowing down. "Mmblbl!" 

Toriel turned to see Frisk struggle, and swam back to help him, bubbling out in reply, "Ghmblbl!" She reached her son and took his hands, making him focus on her calm, yet worried expression. He hugged her in return, as if to apologise for being so slow. Even if she couldn't say it, she was very proud of him for swimming for so long in this predicament. 

She looked to the further reaches of the tunnel and got an idea. The goat rolled onto her front and signalled to the child to climb onto her. Frisk looked at her and slowly understood what she meant, swimming to her person and grabbed her shoulders before pulling himself onto her back, as if to give him a piggyback ride. 

With a smile, Toriel felt the child's legs by her sides and pushing off a rock pillar with her feet, she took off down the chamber, pumping her arms and swimming strongly, much faster now that Frisk was hanging on tight. Even with the young boy on her, her swim speed barely changed at all, and she was able to pull off some good speed for someone her age. Her legs undulated like a dolphin, and was able to propel them both into another tunnel. 

Frisk wrapped his arms around her neck, holding on tight as the goat swam with great speed. The way she kicked and swam through the caves reminded her of those mermaid movies they had watched together. While Toriel wasn't exactly a mermaid, to him she might as well have been. Her soft fur provided a comfortable ride for the child, even if he has to put up with his penis rubbing against the small of her back, making him blush a bit more. It certainly wasn't an unpleasant feeling, but it was new to the child. 

With the young child now hanging on tight to his mother, Toriel took to swimming faster now that she didn't have to worry about her son slowing them down. But the need for air was still very apparent, and it wouldn't be long now until Frisk and Toriel needed to breathe again, especially as the further they swam, the more the pressure around them built. 

They weren't out of the woods just yet.

**Author's Note:**

> Currently writing the second chapter now, so expect that in the future.


End file.
